In hydraulic systems that have rotating components, such as gear shafts and crank shafts, rotating proximate stationary components of the system at an interface, hydraulic system pressure and flow rates can vary with speed of the rotating components. The pressure variance is due to rotational velocity imparted on a fluid control volume affected by the rotating components. The rotational effect on the fluid results in a vortex having fluid pressures that vary from a minimum pressure proximate a longitudinal axis of the rotating component to higher pressures as the control volume extends radially outward from the longitudinal axis. Depending on the geometries of the components, the vortex effect can be impactful to the overall function of the hydraulic system.
In one exemplary hydraulic system, rotating gear shafts in some transmissions have longitudinal shaft bores placing pressurized hydraulic fluid from a control volume in fluid communication with other internal components of the transmission. The pressurized hydraulic fluid from the control volume may be communicated through the longitudinal shaft bore to a balance piston for a clutch that engages and disengages the gear shaft. Hydraulic fluid from the longitudinal shaft bore may provide the necessary pressure to keep the clutch disengaged at appropriate times during the operation of the transmission assembly. At high shaft speeds, the vortex in the control volume may reduce the pressure at the longitudinal axis and the longitudinal shaft bore sufficiently to allow the clutch to engage when the clutch should be disengaged. In these conditions, the pressure of the hydraulic fluid input to the control volume must be increased to raise the pressure within the longitudinal bore shaft to the level necessary to prevent such inadvertent engagement.
Some systems are known where disturbances may be caused in fluids at interfaces involving rotating and stationary components. For example, U.S. Pat. No. 6,621,263, issued on Sep. 16, 2003 to Al-Janabi et al. and entitled, “High-Speed Corrosion-Resistant Rotating Cylinder Electrode System,” discloses a test device with a cell body enclosing a test fluid and having disposed therein, among other components, a stationary reference electrode and a rotating working electrode. A cap on the working electrode has a conical upper surface to minimize artificial disturbances to the fluid flow at the surface of the working electrode. The length of the working electrode is relatively small compared to the depth of the test fluid to further assist in reducing vortex phenomena within the cell body. Though the configuration of the upper surface of the rotating component (working electrode) is configured to minimize disturbances and vortex phenomena in the test device, the rotating component does not have a longitudinal shaft bore as is present in the gear shafts of some transmission assemblies 10 and other rotating-stationary component interfaces. Consequently, it is uncertain whether a pressure could be maintained in a longitudinal shaft bore if a generally planar shaft end surface of a gear shaft were replaced by the conically shaped surface of the Al-Janabi et al. test device. In view of this, a need exists for an improved rotating-stationary component interface that reduces or eliminates vortex flows and corresponding reduced fluid pressure in a control volume proximate a longitudinal axis and longitudinal bore of the rotating component.